Name one war fought by the United States in the 1800s.

The Civil War is indeed one of the significant wars fought by the United States during the 1800s. This conflict, which occurred from 1861 to 1865, was primarily centered around the issues of slavery and states' rights. The war was fought between the Northern states (the Union) and the Southern states that seceded from the Union to form the Confederacy. The outcome of the Civil War had profound effects on the nation, leading to the abolition of slavery, significant social and economic changes, and the beginning of the Reconstruction era.

In contrast, the Revolutionary War took place in the late 18th century, specifically from 1775 to 1783, as the American colonies fought for independence from British rule. World War I occurred much later, beginning in 1914 and involving the United States primarily from 1917 to 1918. The War of 1812, although also a conflict in the 1800s, was a different and separate war fought against Great Britain, and while it fits the timeframe, the Civil War is often highlighted due to its lasting impact on the country.